The present invention relates to a method of and an apparatus for painting or coating an object, and more particularly to a method of and an apparatus for applying a high-quality paint coating to an outer surface of an automotive vehicle body which is being conveyed along a paint coating line.
Automobile industry in recent years employs highly automated line production processes for efficiently mass-producing automobile products. There are used assembling apparatus for assembling individual parts and conveyor apparatus for conveying components to respective working positions. Painting apparatus for painting or coating automobile bodies are also automated.
Various methods have heretofore been employed for automatically painting automobile bodies. According to one known painting method, for example, an automobile vehicle body which has already been coated on its inner surface is conveyed by a conveyor apparatus, and sprays of paint are applied from a plurality of paint spray guns to side panels, an engine hood, a roof, and a trunk lid of the vehicle body as it is conveyed, so that the vehicle body will be coated.
In the above painting method, however, since the vehicle body is coated while it is being conveyed with respect to the fixed painting apparatus, the distance that the vehicle body is conveyed is considerably long. Therefore, the paint coating line takes up a large space, failing to achieve effective utilization of a working space.
Another painting method which has been used keeps an automobile vehicle body at rest in a painting position and displaces a painting apparatus with a plurality of paint spray guns with respect to the vehicle body for coating the same (see Japanese Laid-Open Patent Publication No. 60-25565, for example). The paint spray guns are arranged in an inverted U-shaped, or portal-shaped, pattern so that they confront the side panels and upper panel of the vehicle body. More specifically, the portal-shaped painting apparatus includes two side painting mechanisms located on opposite sides and each having a plurality of paint spray guns, and an upper painting mechanism located on the upper side and having a plurality of spray guns directed downwardly.
The portal-shaped painting apparatus is moved with respect to the stationary vehicle body, during which time paint sprays are applied from the paint spray guns on the upper and side painting mechanisms to the vehicle body.
With this method, however, the painting mechanisms have to travel for a distance corresponding to the length of the vehicle body. This has proven unsatisfactory in view of demands for higher operation efficiency and more effective utilization of working space on the assembly line.
An automotive vehicle body comprises various components such as a relatively horizontal roof, front and rear pillars which are inclined relatively largely, an engine roof, a trunk lid, and other parts. Since these components are different in shape, it is difficult to apply a uniform paint coating to the entire vehicle body. Particularly, a front portion of the engine roof and a rear portion of the trunk lid tend to remain uncoated. It has been necessary to apply a paint coat to those uncoated areas after the vehicle was coated by the painting apparatus. Accordingly, the efficiency of the painting method has been poor.
During the painting process, the paint spray guns are moved at a constant speed in the longitudinal direction of the vehicle body. The surfaces to be coated of the horizontal roof and the front and rear pillars which are largely inclined with respect to the vertical direction are coated at different speeds. Specifically, the speed at which the front and rear pillars are coated is higher than the speed at which the roof is coated. Consequently, when the front and rear pillars are coated, a sufficient paint coating is not applied to their surfaces, with the result that the thickness of the paint coat on the entire vehicle body is liable to be irregular.